When a conventional electronic control unit (ECU) on-off controls a relay as a controlled object, the ECU outputs a control signal to the relay (for example, JP8-192723A). Then, an input voltage that will be inputted into a relay load is fed back from a relay into the ECU. Based on the input voltage, the ECU determines (confirms) whether the relay is actually turned on or off. FIG. 3 illustrates an ON/OFF determination of the relay, which is determined to be turned off when a level of the input voltage that is fed back into the ECU is low. The relay is turned off when the input voltage is at the ground level (i.e., 0 V). The relay is turned on when the input voltage is at a level of a battery supply voltage (i.e., 12 V) of the ECU. Given the above input voltage levels, the relay is determined to be turned on if the input voltage is equal to or higher than an ON determination threshold voltage VON (i.e., 4.2 V), and the relay is determined to be turned off if the input voltage is equal to or lower than an OFF determination threshold voltage VOFF (i.e., 2.8 V). For this reason, it cannot be determined whether the relay is determined to be turned on or off when the input voltage is between VOFF and VON (i.e., when the input voltage is higher than 2.8 V and lower than 4.2 V).
Furthermore, with respect to the conventional ECU, it is possible that the ON/OFF determination of the relay cannot be performed properly when a level of the battery supply voltage +B that is applied to the ECU becomes low because of a deterioration in a vehicular battery, a momentary voltage drop due to cranking, or the like. That is, when the level of the battery supply voltage +B becomes low, the input voltage level of the relay is likely to be erroneously determined by and incorrectly inputted into the ECU, so that an input of appropriate information on a state of a vehicle into the ECU cannot be achieved. For instance, when the battery supply voltage +B of a main body ECU, which controls a vehicle chassis, becomes lower than the ON determination threshold voltage VON (i.e., 4.2 V), the relay will be erroneously determined to be turned off, and incorrect information that the relay is turned off is likely to be inputted into the main body ECU despite the fact that the relay is actually turned on. Hence, the erroneous determination and the incorrect input of a state of the relay will bring about controlling the ECU by use of input values that represent a state of the vehicle, which is different from an actual state of the vehicle. As a result, such control will not live up to users' expectations, and/or the relay will operate improperly on its own (for example, a dome lamp as a relay load may be turned on).
Moreover, there are a mechanism whereby outputs are controlled, and the ECU that determines a state of the controlled object based on an input signal, which is fed back from the controlled object such as a switch. In the mechanism and the ECU above, the input signal that is fed back into the ECU and that indicates the state of the controlled object has an abnormal value (for example, an input value may be indeterminate, or the input value may be fixed either at a high or low level) in an abnormal state due to a disconnection fault or the like in a feedback system. Consequently, a load driving device, which detects a disconnection of a load, has been proposed (for example, JP2001-037069A). According to this device, nevertheless, in an abnormal state of the feedback system wherein the input signal is fed back from the controlled object, the input value that represents an actual state of the controlled object is not inputted into the ECU.
Thus, in the abnormal state of the feedback system, in which the input signal is fed back from the controlled object, although the controlled object is actually controlled properly and is in an appropriate state, yet the input value that represents the different state from the actual state of the controlled object is inputted into the ECU. Accordingly, it is possible that the ECU cannot control an apparatus including the controlled object as the users expect, and that the apparatus may operate improperly on its own resultantly.